Index-signal generating system for multi-beam cathode-ray tubes



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HDD/[7G CIRCUIT M. l. BURGETT, JR., INDEX-SIGNAL GENERATING SYSTEM FOR MULTI-BEAM CATHODE-RAY TUBES Original Filed Dec. 10, 1954 MH Y .am MUR R www m u VBG, H Z mlm I. L v n/ 4 mw m n /IAwi F/gl.

A 2,979,559 Patented Apr. 11, 1961.V

INDEX-SIGNAL GENERATIN G SYSTEM FOR MULTI-BEAM CATHODE-RAY TUBES Monte I. Burgett, Jr.,lThiladelphia, Pa., and William G.

Ehrich, Haddonield, NJ., assignors to Philco Corporation, Philadelphia, Pa., a corporation of Pennsylvania Continuation `of application Ser. No. 474,372, Dec. 10, 1954. Y This application Aug. 2, 1957, Ser. No. 676,468

8 Claims. (Cl. 178-5.4)

This invention relates to electrical systems, the present application being a continuation of our copending appli.- cation Serial No. 474,372, filed December l0, 1954, now abandoned. More particularly, the invention relates to beam-indexing systems for multi-beam cathode-ray tubes.

'Ihe invention is particularly adapted for use in, and will be described in connection with, a vcolor television image display system utilizing a single cathode-ray tube having a beam intercepting, image-forming screen comprising parallel stripes of luminescent material. These stripes are preferably arranged in laterally displaced color triplets, each triplet comprising three phosphor Stripes which respond to electron impingement to produce light of three different primary colors. The uppermost stripe in each triplet may, for example, be' made of a phosphor material cmissive of red light, while the intermediate stripe and the lowermost stripe ofthe triplet may consist of phosphors respectively emissive of green light and blue light.-

The cathode-ray tube may additionally comprise means for producing three electron beams having substantially parallel axes which intersect the image-forming screen. The spacing between adjacent beams at the image-forming screen preferably is made substantially equal'to the spacing between the adjacent phosphor stripes of a color triplet of the screen. A deflection system may be arranged tol deiiect the three electron beams as a group in a manner such that the beamsy trace, in sequential color triplets of the image-forming screen, scanning paths parallel to the color stripes thereof.

From a color television receiver there may be supplied three separate video signals, each indicative of a different primary color component of the televised scene. Each of these signals is supplied to that electrode of the cathoderay tube which serves to control the intensity of the electron beam intended to scan the phosphor stripe emissive of the corresponding color.

For proper color rendition, lit is required that each of the beams be restricted to a scanning path coincident With the corresponding phosphor stripe of each color triplet of the beam-intercepting screen. However, this is not readily achieved without the provision of an auxiliary control system because of practical difliculties arising in the manufacture of the tube and of the detiection system therefor. More particularly, in order to achieve adequate Vertical resolution, and faithful color reproduction in the image formed upon the cathode-ray tube screen, the transverse dimension of each of the phosphor stripes of a given color triplet must be very small-eg., for a cathode-ray tube having a screen 12" high, each of the phosphor stripes must have a width of the order of 0.007".

Moreover it is economically unfeasible to deposit the phosphor stripes in precisely parallel lines so that, even if a linear deflection system were to be provided, accurate scanning of the stripes would not be achieved. In addition, because of the close spacing of the stripes, a slight displacement of the beams in a direction transverse to the color stripes will cause the beams to impinge at least partially on color stripes adjacent the assigned stripes,

thereby causing the image reproduced on the screen of the cathode-ray tube to have incorrect color values.

In order to reduce this color distortion in the reproduced image to tolerable levels, it has been proposed to derive from the image screen an indexing' signal indicative of the instantaneous positions of the cathode-ray beams,

which signal is utilized to'deflect the cathode-ray beams appropriately whenever they depart from thedesired scanning path as determined by the positions of the phosphor stripes. These index signal-'derivingV means may, in one arrangement, utilize the color phosphor stripes per se as a source of beam position information, or, in another arrangement, may utilize, as the source of this information, a plurality of stripe members disposed in a geometric configuration indicative of the geometric coni figuration of the color triplets. In the latter case, the indexing stripes may comprise a material having secondary-emissive properties which diifer from the secondaryemissive properties of the remaining portions of the beamintercepting structure. Alternatively the indexing stripes may consist of a iluorescent material, such as zinc oxide, having a spectral output in the non-visible light region, and the indexing signals may be derived from a suitable photo-electric cell arranged, for example, in a side wall 4 portion of the cathode-ray tube, out of the path of the cathode-ray beams and facing the beam-intercepting surface of the screen structure.

In one such prior-art beam control system, it has been` proposed to index the position of the electron beams by amplitude-modulating the different video signals, applied to the electrodes respectively controlling the intensities of the different beams, with individual high-frequency pilot waves, each having a different frequency. For example, it has been proposed to modulate the video signal applied to the electrode controlling the intensity of the beam intended to excite the central stripe of the color triplet, with a first pilot wave having a given frequency, and to modulate the videosignals applied to the electrodes respectivelycontrolling the intensities of the beams intended to excite different ones of the two peripheral stripes of the color triplet, by second and third pilot waves which respectively have frequencies less than and greater than that of the first pilot wave. By means of a filter designed to pass only light of the colory emitted by the central stripe, and a photoelectric cellvpositioned so as to intercept the light transmitted by the filter, an'output signal is generated having a frequency as determined by which of the beams is incident on the central stripe. This signal may then be supplied to a frequency-responsive detector, the output from which is supplied to the beam deection system to deflect the beams in a sense tending to correct any deviations of the beams from their desired path.

As a practical matter, the aforedescribed beam-indexing system cannot precisely index the beams because of inherent shortcomings of presently available multi-beam cathode-ray tubes. More particularly, these cathode-ray tubes generally exhibit a substantial amount of capacitive coupling between the control electrodes which serve to control thefintensities of each of the beams. Because of this coupling, the intensity of each of the beams is modulated in accordance with pilot waves intended to modulate solely the intensity of other beam. Under these conditions, a spurious signal maybe produced by the beam-indexing system even when the beams are-correctly positioned on the image screen.

In addition, the beam generating systems of the Vtube exhibit non-linear beam-current versus control-voltage characteristics so that the intensity of each of the beams is varied not only in accordance with the modulated combination of the video wave and pilot Wave, but also in accordance with spurious signals having frequencies corresponding to the sum-and-ditference frequencies of the various pilot waves. The difference frequencies generally fall within the video frequency range of the color television system, and as a result the spurious signals having these frequencies produce visible and annoying color distortion of the image reproduced upon the screen of the cathode-ray tube.

Moreover it is found that, since the diameter of the cathode-ray beam at the image-forming screen is of the order of magnitude of the width of a phosphor stripe, and in many instances slightly larger, portions of each of the cathode-ray beams overlap adjacent stripes even when the beams are correctly centered upon the assigned stripes. Under these conditions, a slight mistuning of the frequency-selective network which derives the indexing signal from the output of the photoelectric cell, and/or variations or the relative-intensities of the beams such as occur when producing colors other than white or gray, causeA a false correction signal to be generated. This false signal in turn causes the beam-indexing system to be erroneously actuated, thereby impairing the color rendition of the reproduced image.

In addition to the foregoing, the prior-art system has the disadvantage that it is necessary to control precisely the frequencies of three pilot carrier oscillators, as well as the response characteristic of the frequency responsive element of the control system. Because of these requirements, and because of the need for three separate signal sources, such a system has proved to be economically prohibitive.

Accordingly it is an object of the invention to provide improved cathode-ray tube systems.

A further object of the invention is to provide improved indexing systems for multi-beam cathode-ray tubes.

An additional object of the invention is to provide improved' indexing systems for multi-beam cathode-ray tubes, in which systems video contamination resulting from intermodulation of the pilot waves is absent.

A still further object of the invention is to provide improved indexing systems for multi-beam cathode-ray tubes wherein the relationships to be maintained between the values of various system components are relatively non-critical.

A specific object of the invention is to provide improved indexing systems for multi-beam cathode-ray tubes, wherein spurious error signals, normally produced in response to equi-energy overlapping of the peripheral cathode-ray beams onto the indexing stripes, are substantially eliminated. 1

Another object of the invention is to provide improved indexing systems for multi-beam cathode-ray tubes, which systems are cheap, easily adjusted and hence, commercially valuable.

In accordance with the invention, the foregoing objects are achieved by systems which include a cathode-ray tube having a beam-intercepting member and an electron gun arrangement for projecting toward this member two spaced electron beams. The beam-intercepting member comprises two spaced electron-responsive portions, as well as a third portion positioned between the aforementioned two portions. This third portion is constructed to have a response to electron impingernent different from the responses of the other portions.

In contrast to prior-art arrangements, the intensities of the two electron beams are modulated at the same periodicity, but in phases differing from one another.

By reason of the distinctive response to electron impingement of the aforedescribed third portion of the beam intercepting member, there can be derived from this member a wave having the aforementioned periodicity and a phase whose value is primarily determined by the extent to which each electron beam impinges on the aforesaidV third portion. This wave is supplied to means which produce, a control signal indicative of the phase-value of the wave. This phase-indicative control signal is utilized, in turn, to deflect the two electron beams in a direction transverse to the two portions of the beam-intercepting member.

The invention will be described in greater detail with reference to the appended drawings forming part of the specilication and in which:

Figure l is a block diagram illustrating a preferred form of the indexing system in accordance with the invention; and

Figure 2 is a perspective view of a portion of one form of an image-reproducing screen suitable for use in the novel indexing system shown in Figure 1.

The cathode-ray tube system shown in Figure l comprises a cathode-ray tube 10 containing, within an evacuated envelope 12, a unitary multiple beam generating and controlling assembly comprising a cathode 14, and first, second and third beam control electrodes, designated 16, 18 and 20 respectively, and constructed to control the intensities of rst, second and third cathoderay beams (not shown). Preferably the cathode-ray beams are produced in a manner such that they are substantially parallel and coplanar. The generating and controlling assembly may be of conventional form, one suitable structure therefor being described in the copending application of William E. Bradley, Serial No. 354,588, tiled May 12, 1953, now Patent No. 2,858,364, issued October 28, 1958, and assigned to the assignee of the present application. Alternatively the assembly may consist of three individual beam generating and intenslty controlling gun assemblies arranged in a common plane.

The tube 10 further comprises a focusing electrode 22 and a beam accelerating electrode 24, the latter of which may consist of a conductive coating applied to the inner wall of the envelope and terminating at a point spaced from the end-face 26 of the tube in conformity with well-established practice.

The cathode 14 of the tube 10 is connected to a point `at ground potential, while each of the control electrodes 16, 18 and 20 is established at a negative biasing potential adapted to reduce the intensity of the cathode-ray beam controlled by the given electrode to a small, predetermined value, in the absence of signal potentials upon the electrode. These negative biasing potentials are derived from a biasing network 28 comprising, as a Voltage source, a battery 30 having its positive pole connected to a point at ground potential, and resistors 32, 34 and 36 having adjustable taps 38, 80 and 42 respectively, and connected in shunt with battery 30. Tap 38 is connected to control electrode 16 by an isolating resistor 44, and to a point at ground potential by a by-pass capacitor 46; tap 40 is connected to control electrode 1S by an isolating resistor 48, and to a point at ground potential by a by-pass capacitor 50; and tap 42 is connected to control electrode 20 by an isolating resistor 52, and to a point iat ground potential by a by-pass capacitor 54.

Electrodes 22 and 24 `are maintained at their desircd operating potentials by suitable voltage sources shown as batteries 56 and 58, the battery 56 having its positive pole connected to the focusing electrode 22 and its negative pole connected to a point at ground potential, and the battery 58 having its positive pole connected to accelerating electrode 24 and its negative pole connected to the positive pole of battery 56.

The end faceplate 26 of` tube 10 is provided with a beam-intercepting structure 60, one suitable form of which is shown in Figure 2. In the arrangement shown in Figure 2, the structure 60 is formed directly on the faceplate 26. It should be well understood, however, that the structure 60 may be formed on a suitable lighttransparent base which is independent of the faceplate lattached to the aluminum layer 68.'

26 and may be spaced therefrom. `In vthe arrangement shown, the faceplate 26, which in practice consists of glass preferably having substantially uniform transmission characteristics for the various colors of the visible spectrum, is provided with a plurality of parallelly arranged stripes 62, 64 and 66 ofAphosphor materials which, uponimpingement of an lelectron beam, fluoresce to produce light of'three dilerentprimary colors. For example, the stripe 62 may consist of a phosphor such as zinc phosphate containing manganese as an activator, which upon electron impingement produces red light; the stripe 64 may consist of a phosphor such as zinc orthosilicate, which upon electron. impingementproduces green light; and the stripe 66 vmay consist ofya phosphor such as calcium magnesium silicate containing titanium as an activator, which upon electron impingement produces'blue light. Other suitable materialswhich may be used to form the phosphor stripesl 62, 64 and 66 are well known to those skilled `in the art, as well as methodsV i of Iapplying them to the faceplate 26, and accordingly it is deemed unnecessary to set forth further details concerning them. v

Each of the groups of stripes may be termed a color triplet, and, as will be noted, the sequenceA of the stripes is repeated in consecutive order over :the area of the-structure 60. f. Y., Y 1

- Over all of these phosphor stripesthere is deposited an extremely thin layer of an electron-permeable material 68 such as aluminum, and on top of this aluminum layer 68 are in turn deposited stripes 70,y which parallel the phosphor stripes and are characterized by having av secondary-electron emission ratio; which is substantially different from that of the aluminum layer 68. In the particular arrangement illustrated in VFigure 2, these stripes 70 are disposed at intervals of three phosphor stripes and are located directly above the space between each two adjoining red and green stripes, 62 and 64 respectively. The stripes 70 may be formed of anoxide such ,as magnesium or cesium oxide, or of high Iatomic number metals such as gold, platinum lor tungsten. YThe beam-intercepting structure Y60 so.. Yconstituted is connected to the positive pole of battery 58through a load impedance 72 by 'meansr of -a suitable connector The electron-optical system 4compr1sing the control electrodes 16, 18 and 20, thefocusing electrode 22 and the accelerating electrode'vZl, and the voltages produced by batteries 56 and 58, are adapted to cause the adjacent cathode-ray beams, ie., the first and second cathode-ray beams and the second and third cathoderay beams, to be spaced from one another at the beamintercepting structure `60 by a distance such that the rst, second and third beam may' be positioned substantially at the 'centers of the color stripes 62,64 and 66 respectivelyof any lgiven color triplet. Inordermto deflect the three beams simultaneously .across the faceplate 26 to form a raster thereon, the system is provided with a first deection yoke 74. This yoke is coupled, in turn, to horizontal and vertical sweep-generating c ircuits of conventional design (not shown),

TheAcontrol electrodes 16, 18 and 2,0serving respectively to control the intensities of the first, secondv and third cathode-ray beams, are supplied respectivelyA with red, green and blue video information signals. These signals may be derived from a color television receiver of conventional form (not shown). In the preferredV arrangement shown at Figure 1, the red video information signal is supplied to control electrode 16 through a firstV adding circuit 76, while Vthe green lvideo signal is supplied to control electrode 18 through a second adding circuit '78. The purpose of the of the adding circuits 76 and 78 will becomepapparent -as the description proceeds. l

Ideally, each of the cathode-ray beams, under the influence of the magnetic fieldY produced by the deection yoke 74, tracks centrally along its preassigned phosphor stripe in each color triplet of the. beam-intercepting structure 60. The intensities of the beams are varied, according to the values of the respective video waves, in synchronism with the deflection of the beams, and the video image is reproduced upon the faceplate 26. In practice, however, it is extremely dicult, without further means, to maintain each -beam upon its preassigned color stripe fory each of the hundreds of separate scansions which the beams undergo per frame, as they trace out the raster. y

To insure that the beams traverse their assigned paths, there is provided a` beam indexing system comprising a pilot carrier oscillator 80 and a phase-shifting circuit 82 coupled to the output of oscillator 80. The output of oscillator 80 is coupled to an input of adding circuit 78, while the output of phase shifter 82, is coupled to an input of adding circuits 76. AIn the preferred form of the invention, the oscillator 80 is arranged to produce a pilot carrier having a frequency of 10 mc./ sec., while the phaseshifter 82 is adapted to produce an output signal in phase opposition with the output signal of oscillator 80. However, it should be understoodthat neither the frequency of the pilot carrier nor the amount of phase shift produced by phaseshifter 82 is critical. It is onlyy necessary that the frequency of the pilot carrier lie outside of the range of video frequencies, and that phase shifter 82 produce an output wave shifted in phase by an amount which is substantial with respect to the phase of the carrier produced by oscillator 80.

The system of the invention also comprises an amplifier 84, coupled to the interconnection of Vimpedance 72 and aluminum layer 68 by a capacitor 86 and having a pass band including the frequency of the output signal of the oscillator 80 and excluding frequencies found in the frequency ranges of ,the three `video information signals. The output signal from amplifier 84 is supplied to one input of a phase comparator `88 while, to the other input thereof, is supplied the pilot carrier derivedfrom the output of oscillator 80. v

The output from phase comparator 88 is in turn sup- .plied to a second electromagnetic deflection coil 90 of conventional form, arranged to deect the cathode-ray beams in adirection normal to that of the phosphor strips 62, 64 and 66 and the indexing stripes 70.

As aforementioned, biasing voltages are supplied to control electrodes 16 and J8 having values such that, when no signal is applied to a given one of these electrodes, the intensity of the electron beam controlled by said one electrode is maintained at la low value. The amplitudes of the pilot Waves applied respectively to electrodes 16 and |18 are preferably established so as to be insucientto cut` off the electron beams controlled by ,these electrodes, to be substantially smaller than the average amplitudes of the video information signals respectively supplied to eachof the electrodes, and to produce equi-amplitude variations in the intensities of the electron beams. Y

Y The ladding circuits 76 and 78 may be conventional in form and each may consist, for example, of two electron discharge tubes, each having ya cathode, a control grid and an anode, and wherein the anodes are connected together and to a source .of positive potential, while the cathodes are coupled to a point at ground potential by a common `cathode resistor. In each case, the appropriate pilot Wave is supplied to the grid of one tube;the corresponding video signal is supplied to the grid of the other tube; and the output wave corresponding to the sum of the video signal and the pilot carrier is derived at the common cathode connection of the tubes. `Such adding circuits are described in the publication, Waveforms, edited by B. Chance, V. Hughes, E. F. MacNichol, D. Sayre and F. C. Williams, McGraw-Hill Book Company, Inc., 1949, at page 642 et seq.

The pilot carrier oscillator 8'0, in a typical form, may

1 1 1 fcompriseanfeleetron discharge. devieehavingfitsinput.andi i 1 output electrodes coupled :together in positive feedback f 1 1 1 relationship by: rncansf of a; resonant circuit 1 1 assigned frequency of; the oscillator. 1 1 1 1 1 1 1 1 1 The phase shifterzSZmay have one ofrnany forms, one simple form being that of asingle: stagezamplij '1 tier `coinprfisinganr electronedischarge tube having: a, cath- 1 i 1 ode, azcontrcl gridand an anode, and whereinthe `cathode 1 1 1 is :connected to a :point :of reference potential through la- 1 1 l cathode-biasing resistor.: j'lhe grid is coupled to: the1 outl f put ofoscillator 8g@ andthe anode-isconnected toasouree f 1 1 I pipositivef voltage-through ai load resistor1,;and:is coupled 1 1 ztoan; inputzof adelinacircuit-,745;y Alternatively this :phase shifter may cofmpriseadetay Frequency selectire amplifier: Se may be :ofg conversa, 1

` having suicientgain' 1 1 tional form, andigs: chafa-cteriredbg o amplify; thefindex; Signat derived rom he :load resistor I 1 Alternative1y1y phase; comparator 1r83 may comprise.: 1a 1 pentagridgclectron discharge tube. having: first endg second f :eontroi electrodes, to .onesof which; is supplied the output 1 2 :signal ofdrequency-selective amplifierfdand tothe other 1 i 1 otlwhich fis supplied the pilot carrieri producedbyoscill 1 jlator 50,; The cathodeofthe pentagrigd tube sis1resistiyely 1 coupled to, fa point lat ground :potential while the anode f i thereof gis resistiyely coupled to :a source of positive volte i i 'Iso :theosofie ogf1the1 perrtgajgrid tube iis; coupled; 'a 1 tuned to' the structural Z to: a' eonvenientl1yl usable: level lPhasecornparator; SS may :also 1 :sign 1and may; consist,;t'or :exampiff Di ai bridge; :tlwof arms lopfnyvhich are made upodiode elements' which areeneo; 1 1 [gizedfin phaseoppositinn -byone of theiinputsignals: and= energized in the same phaseby ftheE otherA :of: the 1input1 1 he; phase1comparator1 may lne et' 1 l ls.: In one-form; the type 1d cribed by' hingtoni in the publicatie jgc low passi lter having a highg-requency 1 cut-fotti substam` ly belew; the frequency ci the pilot carriernetwork serving to compensate for the steady-state voltage, present at the anode of the pentagrid tube, in a manner such that, in the absence of an error signal at the output of amplier 84, no correction voltage is applied to coil 90.

In normal operation, the beams controlled by the electrodes 16 and 18 straddle the indexing stripe 70 or energize this stripe to the same extent. Under the former condition, the stripe 70 is not energized, so that no output signal is produced across the impedance 72, and accordingly no output signal appears at the output of phase comparator `8S. Under the latter condition two equi-intensity signals are produced which, however, are of opposite phase. As a result, these signals cancel one another, and no output signal is produced across the impedance 72. Consequently, no output signal appears at the output of phase comparator 88.

However, when the cathode-ray beams are misdellected so that the beam from control electrode 16, normally incident on stripe 62 of the color triplet, falls upon stripe 64 thereof, the beam from control electrode 18, normally incident on stripe 64, falls upon stripe 66, and the beam from control electrode 20, normally incident on stripe 66, falls upon stripe 62 of the succeeding color triplet, the cathode-ray beam controlled by electrode 16 excites the index stripe 70 in its travel from stripe 62 toward stripe 64. Stripe 70, in response to the excitation atorded by this'beam, emits secondary electrons to produce an indexing signal across impedance 72 having a phase corresponding to that of the signal supplied by phase shifter 82 to electrode 16 and an intensity dependent upon the extent to which the respective indexing beams overlap indexing stripe 70. This indexing signal is selectively amplied by amplifier 84 and is supplied to phase comparator 88. Since the amplified inl 1 f :Smlarlyg'when the: beams are misdefleeted; 1opposite tof that: discussed: above?, 1 the: 'cathode-ray beam' line; 'orf a transformer.= g f f 1 1 :y 1

conventional in de-3 1 1 Signat-is produced at'the outputof the :phase comparator; 1 l I 1 'J havinga polarity as determined lby' the :direction ot"` the f 1 excursion of the beam 'ontothe :indexing lstripe 791.: This 1 1 1 output signal in: turn energ'izesy detlection' coil190? to pre1z 1 1 duce a magnetic ft'eld havin'g la 1polarity tending-to delect the beams toward their correct positions-Lie; havl 1 ing; a polarity/ tending to decrease lthe fmagnitudeof; the 1 1 1 fhiand *an indexing 'signal isfaecoringiy generated= across l .impedance :72; 5 The phase of this indexing: signal cor'- 1 responds fte 1the. phase of the signal: produced by :oscil- 1la`tor Sr-5e :it: isii phase opposition to' the indexing 1 signal that would: be produced: in response to the tir catherine-ray; beam; -As a result; 'the control signal ypr duced 1by: phase comparator fSS; in response to: the amp -ti d has apolarity opposite to that Aof 1the control signal cor# responding to: the 5 first beam; and 1th@ magnetici netog projdzufced I by; deflection1 coil 190 1 in response 'o this'? control l igual -deectsjthejeathodef- 1 a; sense tending l to:

'1P0StionS'.=-= 1 I, i 1 1111111323 3131: 31 1 1 i 1 Itwiil fbe zsieeng from fthe foregoing that@ the lsfr/'stem of the invention; hasthe advantage: tasti neither' :the 'fre-1 :quency :nor the: atnpitide iof 1 the signal produced by o`s icifliator; 8:0 needs 1to1 he: controlled2 t'o' close? 'tolerance rallies, :because: e. change in :either of? 1these l v win be reneeted equally throughout: the: phaseicemparl 1 1 1 r son system; 1 Additionally; inasmuch: 'as luie j pifot jaar-1 1 1 grijerfsf for; each of the beams f have luie same? frequence, :only one pilot: earriery sourcejisf :require 1 electron guns :cannot1 result in the production of spurious 1 l i 1 1 dexingsignal is; in phase :opposition 1 toi the: pilot carrier 1 Supplied to zcomparator 188 by f oscillator 8o,- a: control' output lsignal from 1phase1 comprtor :88.1 l 1 l 1 1 1 1 1 1 1 ina sense? 1 1 1 l controlled by aelectrode 13 falls upon :the :index: s'tfripe indexing; Signat corresponding :to 1 the 'secondi be y; beams in use riding e magnitude of the control. signalie., in 1 restore. the: beams' ito their lassi'gpefd referees Furthermofr 1e frequency; crajpe entre; coupling of the various' `pilot waves lbetween; the

ecaus'e; the pilot carriers have Etjlie signals corresponding to the diiference frequencies between pairs of pilot waves. The phase comparator 88 is simple and does not involve the use of tuned circuits to establish its condition of zero output.

While the foregoing description relates to a system according to the invention in which three cathode-ray beams are indexed, it is obvious that the system of the invention can serve equally well to index two, or more than three beams. In addition, while the invention has been described with reference to the specific beam-intercepting structure 60 illustrated in Figure 2, it is to be well understood that it is equally applicable to systems comprising other beam-intercepting structures. For example, the beam-intercepting structure 60 may be of a form wherein the lindexing stripe 70 is positioned coincident with the green phosphor stripe 64. In this case, the pilot signals would be applied additively to the control` electrodes 16 and 20.

Alternatively, the indexing stripes 70 can be dispensed with entirely, and a photo-electric detector employed. In this case a photocell, actuated selectively by the green phosphor stripe, may be used to produce the indexing signal. This signal would then be supplied to the amplitier 84, and the system would function in a manner similar to that described above.

In addition, while in the preferred embodiment the pilot Waves supplied respectively to control electrodes 16 and 18 are additively combined with the corresponding video signals, it will be Well understood that, in each case, the pilot wave and video signal may be combined multiplicatively. Moreover, While in the preferred embodiment, the amplitude of each pilot wave is related to the quiescent intensity of the corresponding cathoderay beam in a manner such that the beam is never cut off by the pilot wave, it is clear that the quiescent beam intensity and the amplitude of the pilot wave may be adjusted so that pulses of beam current corresponding tothe positive-going peaks of the pilotwave are produced in place of the continuously varying'beam current.

Additionally, while in the preferred embodiment of theinvention the two pilot waves supplied to the control electrodes 16 and 18 are caused to have opposite phases, it is clear that, in general, the phase difference between these two waves may be any inite value. In those cases where this phase difference is an angle other than 180, it is desirable to interpose a phase-shifting network (not shown) between the output of pilot carrier oscillator 80 and the input of phase comparator 88, adapted to shift the phase of the reference signal supplied to phase comparator 88 by an amount equal to 90 plus one-half of the sum of the phases ofthe two pilot waves.

Furthermore, while in the system as described the positions of the cathode-ray beams are altered in accordance with the output signal of phase comparator 8S by means of an auxiliary deiiection coil 90, it is obvious that alternatively the positions of the beams can be controlled by supplying the'output signal of comparator 88 to the detiection coil 74 or to electrostatic deflection plates (not shown) suitably mounted within cathoderay tube 12.

Whilelwe have described our invention by means of specific examples and in a specific embodiment, We do not wish to be limited thereto, for obvious modifications will occur to those skilled in the art without departing from the spirit and scope of the invention.

What we claim is: Y

1. A television system comprising a cathode-ray tube having means for producing two spaced electron beams, means for individually controlling the intensity of each of said beams and a beam-intercepting screen member, said screen member comprising a plurality of parallel stripegroups, each of said stripe-groups comprising iirst and second stripe-members responsive to electron impingement to emit light of respectively first and second colors and a third stripe-member arranged intermediate said iirst and second stripe-members, said third stripe-member having a response to electron impingement different from that of said irst and second stripe-members, means for supplying a iirst intelligence wave yindicative of the content of a televised scene of said irst color and consisting of components having frequencies within a first frequency range, means for generating a first pilot wave having, a given phase and a given periodicity falling outside of said given frequency range, means for combining said iirst intelligence wave with said first pilot wave to form a rst composite signal, means for supplying said first composite signal to the intensity-Varying means for said rst beam, means for supplying :a second intelligence wave indicative of the content in a televised scene of said second color and consisting .of components within a second given frequency range excluding said given periodicity, means for generating a second pilot wave having a phase diiering from said given phase by a preassigned amount and having said given periodicity, means for combining said second intelligence wave with said second pilot Wave to form a second composite signal, means for supplying said second composite signal to the intensity-varying means for said second beam, means for maintaining the intensitiesl of said rst and second beams respectively at preassigned finite values when said first and second composite signals each have zero amplitudes,means for establishing the amplitudes of said-first and second pilot waves .at respective values such that the variations in the intensities of said first and second beams in response thereto occur over a range consisting of finite,nonzero beam intensities, means for deecting said two electron beams over said beam-intercepting screen member in a manner such that said beams trace, in predetermined stripe-groups of said beam-intercepting member, scanning paths parallel to said stripe-members thereof, means coupled to said beam-intercepting screen member for Ideriving a third wavewhose components havemeans for producing aA control signal indicative of the phase of said third wave, and means responsive to said control signal for deecting said two beams in a direction transverse to the orientation of said stripe groups.

2. A television systemv according fto`c1aim 1 wherein said third stripe-member comprises a secondary-electron emissive member, and wherein said third-wave-deriving means comprises a member responsive to secondary-electron emission.

3. A television system according to claim 1 wherein said irst and second frequency ranges respectively of said first yand second intelligence waves are substantially coincident.

4. A television system according to claim l wherein said means for combining said rst intelligencewave and said iirst pilot wave include means for adding said waves, and

` wherein said means for Icombining said second intelligence Wave and said second pilot wave include means for adding said latter waves.

,5. A television system according to claim l wherein said control signal-producing means comprises means for producing a reference wave having said given periodicity and a phase of predetermined value, phase-comparison means supplied with said reference wave and with said third wave, yand means coupling the output of said phase comparison means to said means for deecting said two beams in said transverse direction.

Y 6. A television system according to claim 5 wherein said means for generating said first pilot wave comprises a source of a sinusoidal wave having said given periodicity and phase, wherein said means for producing said second pilot wave (comprises a network supplied with said irst wave and constructed to shift the phase thereof by substantially and wherein said means for producing said Vreference wave comprises said source.

7. A color television system comprising a cathode-ray tube having means for producing first, second and third parallel coplanar spaced electron beams, a beam-intercepting screen member comprising a plurality of consecutive parallel stripe-groups, each of said stripe-groups comprising rst, second and third parallel stripe-members responsive to electron impingement to emit light of respectively iirst, second and third colors, and a fourth stripemember arranged between said second and third stripemembers and responsive to electron impingement to emit secondary electrons, means for individually controlling the intensities of said iirst, second and third beams, means for supplying to the intensity-controlling means for said first beam a first intelligence wave indicative of the content of said iirst color Iin a televised scene and consisting of components in a given frequency range, a first adding circuit having its output coupled to said intensity-varying means for said second beam, means for supplying to an input of said iirst adding circuit a second intelligence wave indicative of the content of said second color in said televised scene and consisting of components in said given frequency range, a source off a first sinusoidal wave having a given frequencyv outside of said given frequency range and a given phase, means coupling the` output of said source to a second input of said first adding circuit, a second adding circuit having its output coupled to said intensity-varying means for said third beam, means for supplying to an input of said second adding circuit a third intelligence wave indicative of the content of said third color in said televised scene and consisting of components in said given frequency range, la phase-shifting network coupled to the output of said source and constructed to produce and supply toa second input of said second adding circuit a second sinusoidal wave having a frequency equal -to said given frequency and a phase substantially in opposition to said given phase, means for maintaining the intensities of said second and third beams respectively at preassignednite values when the output signals of said first and second adding circuits each have zero amplitudes, means for establishing :the amplitudes of said first and second sinusoidal Waves at respective values such that the variations in the intensities of said second and third beams in response thereto occur over a range consisting of iinite, non-zero beam intensities, means for deecting said three electron beams in a manner such that said beams trace, in predetermined stripe-groups of said beam-intercepting member, scanning paths parallel to said stripe members thereof, means responsive to secondary electrons for deriving an output signal from said beam-intercepting screen member, an ampliiier coupled to said deriving means and constructed to transmit signals having frequencies in a second range including said given frequency and excluding said given frequency range, phase-comparator means having one input coupled to the output of said amplifier and another input coupled to the output of said source, means for deflecting said three beams in a direction transverse to the orientation of said stripe-members, and means coupling the output of said phase-comparator means to said last-named deflection means in a polarity such as to cause deflection of said beams in a sense tending to minimize the amplitude ofthe output signal of said phase comparator means.

8. In a color television system wherein three electron beams are directed at a luminescent screen consisting of three sets of a multiplicity of substantially horizontally oriented strips respectively capable of producing light of dierent component colors when excited by the electron beams in a manner to scan a raster on the said screen with horizontal and vertical deection motion, a pilot signal source of specied frequency, means for applying the pilot signal as superimposed modulation at a iirst phase on one of the said three electron beams, means for applying ythe same pilot signal at the same frequency as superirnposed modulation at a second phase on another of said three electron beams, means on the luminescent screen including a set of secondary electron emission strips whose emission diers from that of the surrounding material aligned over the horizontal light producing strips of the screen which are intended to be excited by the electron beam which has no pilot frequency modulation adapting the strips to produce secondary emission electrons when struck by the electron beams, means for producing secondary emission electrons with pilot frequency modula tions at substantially the first or second phases respectively when the electron beams modulated by the pilot frequencies at the respective phases strikes the secondary electron emission strips, a collector electrode with means adapting it to produce phased electrical error signals in accordance with the phase of the secondary emitted electrons, a phase detector with means to demodulate the electrical error signals from the collector electrode producing error voltages of a polarity in accordance with the sense of the phase, and means responsive to the error voltages to alter the ventical deflection of the electron beams to correct errors of registration.

References Cited in the le of this patent UNITED STATES PATENTS 2,587,074 Sziklai Feb. 26, 1952 2,671,129 Moore Mar. 2, 1954 2,727,184 Miller et al Dec. 13, 1955 2,737,608 Sziklai Mar. 6, 1956 2,763,715 Fromm Sept. 18, 1956 2,792,521 Sziklai et al May 14, 1957 

